The present invention relates in general to air conditioning systems and, particularly, to a central air conditioning system of, for example, a single-duct design. More particularly, the present invention is concerned with a method of re-conditioning air which has been supplied from such a system and circulated through a space or spaces to be heated or cooled and further with an air conditioning unit for use with the system to carry out the method into practice.
While the central air conditioning system incorporating the improvement according to the present invention may be useful for the comfort cooling and heating of residential buildings and premises or for district air conditioning purposes, the same will prove advantageous particularly when installed in relatively large-sized, multiroom and/or multistory structures such as business, commercial, industrial, institutional or public buildings as will be understood as the description proceeds.
The capabilities, performance characteristics and dimensional details of a single-duct central air conditioning system are usually determined in the process of planning and designing the building in which the air conditioning system is to be installed. When the building is completed and transferred to the client or to tenants of the client from the contractor, it is usual that the users of the building have the floors or the existing compartments of each of the floors partitioned into sections and subsections depending upon the purpose for which the floor spaces are to be utilized. This results in change in the distribution of conditioning air supplied from the central conditioning unit and circulated through the spaces in the floors. The draughts of air into the spaces to be conditioned therefore vary from one section or subsection to another and, in the worst case, there will be such sections or subsections that are not directly ventilated from the distribution ductwork of the air conditioning system and are thus not or, at most, only poorly air conditioned. Such localized distribution of conditioning air also results from the sensible loads located in the space or spaces to be air conditioned, such as heat-emanating or heat-absorbing equipment and appliances, illumination for the space or spaces, and gains or losses of heat due to solar and sky radiation through the envelope of the building such as the roof structure, exterior walls, window panes and other kinds of skins.
To remedy the localized distribution of the conditioning air, it has been an ordinary practice to have the air distribution ductwork of the conditioning system locally re-arranged so as to compensate for the change in the load. This will compel the owner or the tenants of the building to incur extra expenses. Because, moreover, the ductwork is re-arranged only locally for the purpose of saving the cost and because of the fact that the central air conditioning unit per se is usually not re-adjusted or exchanged, the initially designed balance of the system tends to be destroyed even after the ductwork is re-arranged and, as a consequence, there will still exist sections or subsections which are only poorly air conditioned or the capacity of the system per se will become short of meeting the total demand of the building.
These problems may be solved if the air conditioning is "zoned" by arranging the single-duct system with supplementary terminal re-heating or re-cooling fan-coil units each to care for one or more of the zones or with manually or automatically controlled air-volume regulators to care for the individual sections or subsections. As an alternative, a dual-duct air conditioning system may be utilized in which warm and cold air from the central air conditioning unit served through parallel trunk supply systems is mixed by dampers delivering air properly proportioned to meet the different demands of the individual zones. Application of these types of air conditioning systems to large-sized buildings still presents a number of problems that must be solved. Among these problems are (1) the various kinds of losses of heat and pressure as caused by the transmission and delivery of the streams of the conditioning air through the ducts, the re-heating or re-cooling of air from the central unit, and the mixing of hot and cold air; (2) the increased installation and maintenance costs; (3) the complexity of the system arrangement; (4) the skilful techniques and the sustained, scrupulous maintenance and servicing required to enable the system to properly operate under varying environmental and weather conditions; and (5) the limited allowance for the extension and re-arrangement of the ductwork, the terminal devices, or the central unit.
To overcome all these problems that have been encountered in the prior art air conditioning systems for installation in large-sized buildings, the present invention proposes a central air conditioning system which is arranged with local air conditioning units mounted within ceiling structures above the spaces to be air conditioned, using the chamber in each ceiling structure as part of the air distribution ductwork. A ceiling mounted air conditioner per se is well known in the art as from U.S. Pats. Nos. 2,682,757, 2,770,955, 2,817,217 and 3,625,022. Problems are, however, pointed out in respect of any of the ceiling attic installed air conditioners taught in these patents in that the heat exchange efficiencies on both heating and cooling cycles are low because outdoor air is used, without being pre-heated or precooled, as a source of heat or a medium to be heated by the rejected air and in that additional cost and space are required for the installation of the piping to drain off water condensate produced onto the condenser coil of the conditioner.